Illustrated herein in embodiments are liquid crystal displays (LCDs) and, more particularly, cholesteric multi-color liquid crystal displays.
Cholesteric liquid crystal displays have attracted attention in recent years as an electronic paper (e-paper) type of display device. It would be particularly advantageous to develop an effective and inexpensive multi-color e-paper. However, successful demonstrations of cholesteric multi-color displays have so far involved a three-layer stack of cholesteric displays, with each layer reflecting a primary color, e.g. red, green or blue. Unfortunately, this type of a display is comparatively expensive and consumes a great deal of power, rendering it unsuitable for inexpensive portable displays utilizing battery power. A single-layer cholesteric color display would be less expensive to manufacture and more suitable as a multicolor electronic paper, requiring less power to operate than a three-layer design while, at the same time, being more flexible and durable than a three-layer design.
Color change of a single-layer cholesteric display has been previously demonstrated by switching with an electric field with voltages in the 300V range. However, such high voltage requirements are not suitable or practical for battery operated portable displays. Another known method involves a photochemical color change. Unfortunately, this involves an hours-long process to generate a display image, and the image is subject to later pollution and degradation from ambient light. Still another method produces a color change when polymeric cholesteric flakes suspended in an inert fluid are rotated by an applied electric field. However, it is very difficult to prepare the polymeric cholesteric flakes in the very narrow size distribution required, and different size flakes rotate at different voltage levels, making the display difficult to control.
Therefore, there is a need for a single-layer cholesteric multi-color display with a lower operating voltage than presently required, thereby also providing a more practical embodiment of multi-color electronic paper which consumes less power than present designs.